Method of forming a switched mode power supply controller device with an off mode and structure therefor

ABSTRACT

At least one embodiment is directed to a semiconductor voltage controller comprising: a start-mode circuit associated with a start-mode; and an off-mode circuit associated with an off-mode, where the voltage controller can be configured to receive a feedback signal and an off-mode signal from a single input and provide an output voltage, where the voltage controller can be configured to be in the off-mode when the feedback signal is less than a skip level and the feedback signal is less than a HV control level, and where the voltage controller can be configured to be in start mode when the feedback signal is greater than HV control level and Vcc is below a Vcc-start.

BACKGROUND

The present invention relates, in general, to electronics, and moreparticularly, to semiconductors, structures thereof, and methods offorming semiconductor devices.

Current switch mode power supply controllers seek to maintain an outputvoltage level within a range (e.g., within Vcc-stop and Vcc-start), andsend drive signals to regulate voltage within the range. Such regulationoccurs whether an initially applied load changes or not, for example ifinitially there can be a load voltage on the system, the system willregulate the output voltage to provide the load voltage. However ifconditions change so that there can be no longer any load for period oftime, typical controller systems are unable to provide an off mode thatallows the output voltage to drop outside of the range while there canbe little load voltage and to quickly provide regulation again when aload can be redetected. If an off-mode can be provided typically itsimplementation requires an additional pin to a chip configuration thatprohibits a simple plug and play implementation with existing pinconnections, thus making such solutions difficult to implement inunmodified systems.

Accordingly, it can be desirable to have a method of providing anoff-mode in a power controller where the semiconductor configurationdoes not require any additional pins to implement the off-mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of present invention will become more fully understood fromthe detailed description and the accompanying drawings, wherein:

FIG. 1 schematically illustrates an embodiment of a portion of a systemin accordance with an embodiment of the present invention;

FIG. 2 schematically illustrates an embodiment of a portion of a systemin accordance with an embodiment of the present invention;

FIG. 3 schematically illustrates an embodiment of a portion of a circuitthat can be a portion of the system of FIG. 2 in accordance with anembodiment of the present invention;

FIG. 4 schematically illustrates an embodiment of a portion of a circuitthat can be a portion of the system of FIG. 2 in accordance with anembodiment of the present invention;

FIG. 5 schematically illustrates an embodiment of a portion of a circuitthat can be a portion of the system of FIG. 2 in accordance with anembodiment of the present invention;

FIG. 6 illustrates a portion of signals that can occur during a portionof the operation of a portion of a system of an embodiment of thepresent invention;

FIG. 7 illustrates a portion of signals that can occur during a portionof the operation of a portion of a system of an embodiment of thepresent invention;

FIG. 8 schematically illustrates an embodiment of a portion of a circuitthat can be a portion of a system in accordance with an embodiment ofthe present invention;

FIG. 9 schematically illustrates an embodiment of a portion of anintegrated circuit that can be a portion of a system in accordance withan embodiment of the present invention;

FIG. 10 schematically illustrates an embodiment of a portion of acircuit that can be a portion of a system in accordance with anembodiment of the present invention;

FIG. 11 schematically illustrates an embodiment of a portion of acircuit that can be a portion of a system in accordance with anembodiment of the present invention;

FIG. 12 schematically illustrates an embodiment of a portion of acircuit that can be a portion of a system in accordance with anembodiment of the present invention;

FIG. 13 schematically illustrates an embodiment of a portion of a systemin accordance with an embodiment of the present invention;

FIG. 14 schematically illustrates an embodiment of a portion of a systemin accordance with an embodiment of the present invention;

FIG. 15 schematically illustrates an embodiment of a portion of anintegrated circuit that can be a portion of a system in accordance withan embodiment of the present invention;

FIG. 16 schematically illustrates an embodiment of a portion of anintegrated circuit that can be a portion of a system in accordance withan embodiment of the present invention; and

FIG. 17 illustrates a portion of signals that can occur during a portionof the operation of a portion of a system of an embodiment of thepresent invention.

DETAILED DESCRIPTION

For simplicity and clarity of the illustration, elements in the figuresare not necessarily to scale, are only schematic and are non-limiting,and the same reference numbers in different figures denote the sameelements, unless stated otherwise. Additionally, descriptions anddetails of well-known steps and elements are omitted for simplicity ofthe description. As used herein current carrying electrode means anelement of a device that carries current through the device such as asource or a drain of an MOS transistor or an emitter or a collector of abipolar transistor or a cathode or anode of a diode, and a controlelectrode means an element of the device that controls current flowthrough the device such as a gate of an MOS transistor or a base of abipolar transistor. It will be appreciated by those skilled in the artthat the words “during”, “while”, and “when” as used herein relating tocircuit operation are not exact terms that mean an action takes placeinstantly upon an initiating action but that there may be some small butreasonable delay, such as a propagation delay, between the reaction thatcan be initiated by the initial action. Additionally, the term “while”means that a certain action occurs at least within some portion of aduration of the initiating action. The use of the word “approximately”or “substantially” means that a value of an element can have a parameterthat can be expected to be close to a stated value or position. However,as can be well known in the art there are always minor variances thatprevent the values or positions from being exactly as stated. It can bewell established in the art that variances of up to at least ten percent(10%) (and up to twenty percent (20%) for semiconductor dopingconcentrations) are reasonable variances from the ideal goal of exactlyas described.

When used in reference to a state of a signal, the term “asserted” meansan active state of the signal and inactive means an inactive state ofthe signal. The actual voltage value or logic state (such as a “1” or a“0”) of the signal depends on whether positive or negative logic can beused. Thus, “asserted” can be either a high voltage or a high logic or alow voltage or low logic depending on whether positive or negative logiccan be used and negated may be either a low voltage or low state or ahigh voltage or high logic depending on whether positive or negativelogic can be used. Herein, a positive logic convention can be used, butthose skilled in the art understand that a negative logic conventioncould also be used. The terms “first”, “second”, “third” and the like inthe Claims or/and in the Detailed Description of the Drawings, are usedfor distinguishing between similar elements and not necessarily fordescribing a sequence, either temporally, spatially, in ranking or inany other manner. It can be to be understood that the terms so used areinterchangeable under appropriate circumstances and that the embodimentsdescribed herein are capable of operation in other sequences thandescribed or illustrated herein.

In addition, the description illustrates a cellular design (where thebody regions are a plurality of cellular regions) instead of a singlebody design (where the body region can be comprised of a single regionformed in an elongated pattern, typically in a serpentine pattern).However, it can be intended that the description can be applicable toboth a cellular implementation and a single base implementation.

In all of the examples illustrated and discussed herein, any specificmaterials, such as temperatures, times, energies, and materialproperties for process steps or specific structure implementationsshould be interpreted to be illustrative only and non-limiting.Processes, techniques, apparatus, and materials as known by one ofordinary skill in the art may not be discussed in detail but areintended to be part of an enabling description where appropriate. Itshould also be noted that the word “coupled” used herein implies thatelements may be directly coupled together or may be coupled through oneor more intervening elements. Additionally the term “configured” canrefer to a hardware configuration that can be designed to provide a setof functions when operating, however does not require that the device bepowered, only that the device can be “configured” to perform a functionwhen powered. Thus a claim referring to a system configured to perform afunction can be intended to encompass the system that can be designed toprovide the function, whether or not powered, and such a system does notneed to be powered to infringe the claim.

Note that similar reference numerals and letters refer to similar itemsin the following figures. In some cases, numbers from priorillustrations will not be placed on subsequent figures for purposes ofclarity. In general, it should be assumed that structures not identifiedin a figure are the same as previous prior figures.

FIG. 1 can be an illustration of a switching power supply 100 includingan output 102 in accordance with an embodiment. The output 102 can havea voltage Vcc that can be maintained within a predetermined voltagerange during operation of a switch mode process. The predeterminedvoltage range can vary depending on the application and requirements ofswitching power supply 100. In the example, switching power supply 100represents a common configuration comprising two stages of control. Afirst stage can be a power factor correction (PFC) stage 104 and asecond stage can be a pulse width modulating stage 108. Note howeverthat other embodiments may or may not include a PFC stage 104. Ingeneral, stages 104 and 108 increase the efficiency of the switchingpower supply 100 through active adjustments based on detected input andoutput conditions. In the example, switching power supply 100 can becoupled to an AC voltage, which can be rectified, filtered, and providedto the PFC stage 104 as an input voltage. PFC stage 104 generates aregulated voltage that can differ from the output voltage of powersupply 100. PFC stage 104 can be isolated from the PWM stage 108 by adiode. PFC stage 104 regulates by enabling and disabling a switch 106.The diode when forward biased conducts current from PFC stage 104charging a storage capacitor. As shown, the switch can be a transistorthat can be controlled by the power factor correction stage 104 thatadjusts a duty cycle of the enabled switch 106 in response to a signalcorresponding to the regulated output voltage produced by PFC stage 104.More specifically, power factor correction makes adjustments to maintainan input current including a relationship in time and amplitude with therectified input voltage provided thereto and with the output currentdrawn therefrom. The power factor correction circuitry typically keepsthe power factor as close to unity as possible.

A second stage of switching power supply 100 can be a pulse widthmodulating (PWM) stage 108. PWM stage 108 comprises pulse-widthmodulating control circuitry, a switch 110, and a transformer 112. Thestorage capacitor can be coupled to a first terminal of the primarywinding of the transformer 112. As shown, the switch 110 can be atransistor. The switch 110 can be coupled to a second terminal of theprimary winding of the transformer 112. PWM stage 108 enables anddisables the switch 110 based on an error signal. The error signalcorresponds to a difference in the expected regulated output voltage ofswitching power supply 100 and the output voltage Vout. The voltage atthe output Vout of switching power supply 100 varies over time due tovariations in the loading at the output 102A. The loading at the output102A of power supply 100 can vary from a no-load scenario to loadingthat approaches the maximum current rating. For example, if the loadingon Vout increases, the PWM stage 108 detects the change and responds byraising the duty cycle to deliver power more frequently to the load andmaintain or increase Vout. Conversely, the PWM stage 108 under reducedloading will lower the duty cycle to a level that maintains regulation.In general, the stages 104 and 108 will maintain the voltage at output102A within the predetermined voltage range dictated by the power supplyapplication.

PWM stage 108 can generate a regulated output voltage that differs fromthe regulated output voltage from PFC stage 104. The regulated outputvoltage from PWM stage 108 can be provided through the transformer 112and output rectifier 114A. A storage capacitor 116A can be coupled tothe output rectifier 114A. In the example, transformer 112 can be usedto further modify the output voltage from PWM stage 108 to the regulatedoutput voltage Vout of switching power supply 100. For example,transformer 112 can step down the voltage at the output Vout a multipleof the voltage delivered across the primary winding. As mentionedpreviously, the secondary transformer winding of transformer 112 can becoupled to output rectifier 114A. In the example, output rectifier 114Acan be a rectifier diode including an anode coupled to a secondarytransformer winding and a cathode to the regulated output voltage Vout.The storage capacitor 116A can be coupled to Vout to provide power tothe load when not being delivered by stages 104A and 108. A resistordivider generates a voltage corresponding to the voltage at Vout thatcan be used to monitor changes. As shown, the changes in voltage acrossthe resistor divider generates an error signal that can be coupledoptically to a feedback pin (FB) or a feedback node of an On/OffControl+Feedback Circuit 118. For brevity, On/Off Control+Feedbackcircuit 118 will be called Feedback Control Circuit (FC) circuit 118hereinbelow.

The output rectifier 114A can have two modes of operation in theswitching power supply 100. In a first mode of operation, the outputrectifier 114A can be in a high current path for driving the loadcoupled to the output Vout of switching power supply 100. The outputrectifier 114A can couple PFC stage 104 and PWM stage 108 to the loadthrough transformer 112 when the output rectifier 114A is forwardbiased. In a second mode of operation, the output Vout can be isolatedby output rectifier 114A from PFC stage 104, PWM stage 108, andtransformer 112. As mentioned previously, the storage capacitor 116Acoupled to the output Vout delivers power to the load in the second modeof operation. The output rectifier 114A can stand off significantvoltages while maintaining isolation between the output Vout and theregulation circuitry.

At least one embodiment includes a circuit and method for a highefficiency switch mode power supply including an off-mode. The off-modecan be integrated with additional circuitry that requires no additionalpins to be added to the switch mode power supply controller integratedcircuit. The different modes of operation are controlled through afeedback pin or feedback node of the switch mode power supply used forregulating the circuit. In one embodiment, the switch mode power supplycontroller can have three different modes of operation. In the firstmode, a start process can be initiated. The start process occurs whenthe power supply is first turned on or after an off-mode. The startprocess provides a current to the Vcc 102 of the switching power supply100 thereby moving the voltage Vcc towards the predetermined voltagerange to maintain while under regulation during a switch mode process.In the currently discussed non-limiting example there is no feedbacksignal applied in the off-mode. In a second mode, the switch modeprocess can be enabled to support regulation at the output 102A of theswitching power supply 100. Energy transfer occurs from transformer 112to maintain the output 102A within the predetermined voltage range. Asdisclosed above, the duty cycle of the energy transfer changes withloading. For example, a high duty cycle can be required when theswitching power supply 100 is heavily loaded requiring frequent energytransfer to maintain the voltage Vout within the predetermined voltagerange. Alternatively, a light loading at output 102A requires a low dutycycle or infrequent energy transfer to maintain the voltage Vout withinthe predetermined voltage range. In the example, the feedback signal canbe coupled to node 122 that will vary in magnitude such that the switchmode power supply controller can be enabled or disabled duringregulation. Disabling the switch mode power supply controller stops theswitch mode process thereby preventing the transfer of energy via thesecondary winding of transformer 112 to the output 102A. As shown, acondition or status circuit 130 can be operatively coupled to node 122for changing the mode of operation of power supply 100 via the feedbackpin or feedback node. In one embodiment, the circuit 130 can beoptically coupled to transistor 132 including a collector that can becoupled to the node 122. The third mode can be the off-mode thatprevents the transfer of energy to the output 102A of the switchingpower supply 100. The off-mode will be explained in more detail hereinbelow. In the off-mode, the voltage Vout at the output 102A of the powersupply 100 can be allowed to fall outside of the predetermined voltagerange, for example below the minimum voltage of the predeterminedvoltage range.

The off-mode can be a condition or operative mode of switching powersupply 100 under a no-load condition. In general, the no-load conditionoccurs when little or no power is being delivered from the switchingpower supply 100 to a device coupled to the output 102A. Examples of ano-load condition comprises no device coupled to output 102A, the devicecoupled to output 102A can be turned off, or the device coupled to theoutput can be put into an energy conservation mode. The off-mode can beinitiated when the no-load condition can be detected and a no-loadsignal can be provided to the node 122 that places the power supply 100in the off-mode. The FC circuit 118 can be easily adapted to differentswitching power supply controller designs. The FC circuit 118 typicallyreduces power consumption to various designed levels, for example lessthan 30 milliwatts in the off-mode. Furthermore, in at least oneembodiment the circuit works with a standard pin out of a switch modepower supply controller that does not include an off-mode. No additionalpins are needed. The start mode, feedback mode, and off-mode can beimplemented through the feedback path of the switch mode power supplycontroller. One benefit besides lower energy use is that manufacturerscan retrofit to a new controller including off-mode without the redesignof their interface to a power supply system and more particularly theprinted circuit board. Maintaining the form factor and pin out of theexisting controllers reduces cost and lowers barrier to adoption whileproviding substantial long-term energy savings. A further benefit isthat the over voltage protection or over current protection can be keptin place with no change in performance thereby maintaining existingsafety behaviors.

The off-mode improves the efficiency of the switching power supply 100by preventing the transfer of power to the output 102A for an extendedperiod of time. The time between power transfers to adjust a voltage atthe output 102A in off-mode can be greater than a switch mode powersupply operating normally without off-mode capability. The switchingpower supply 100 dissipates minimal power during the off-mode therebyimproving overall efficiency of the system over time. In the off-mode,the voltage at output 102A will decline over time albeit atsignificantly slower rate than when delivering power to a device.Leakage current and the feedback circuitry loading the output 102A causea slow decline in output voltage. In one embodiment of the off-mode, thevoltage at output 102A can fall below the predetermined regulatedvoltage range maintained during the switch mode process (˜ from 30 s to30 minutes).

In the off-mode, the voltage at output 102A continues to decline until astart mode occurs whereby current can be provided to the output 102A.The start mode is disclosed in more detail in subsequent figures below.The current provided to the Vcc 102 comes from a source other than theswitch mode process. The start mode can be then disabled after thevoltage at the Vcc 102 rises to a level that enables the switch modeprocess thereby transferring energy via the transformer 112. It shouldbe noted that the time from off-mode to enabling the switch mode processcan be accomplished in a very short period of time (˜100 ms). This canbe desirable as the switch mode power supply can rapidly change from avery power efficient state to providing current to a load with aregulated output voltage to enable a device (e.g. the load) in theshortest possible time. The voltage at output 102A will remain withinthe predetermined voltage range during regulation. If a no-loadcondition continued to exist, the switch mode process would remaindisabled such that no energy can be transferred by transformer 112. Thevoltage at output 102A will continue to decline until the start modeoccurs again as disclosed above. Similar to the off-mode, can be astandby, skip, or light load mode. The difference between the off-modeand the standby mode can be that the start mode may not be initiated.The switch mode process can be enabled periodically for a minimal timeperiod to maintain the voltage at output 102A within the predeterminedrange.

In one embodiment, the FC circuit 118 can be integrated with othercircuitry of a switch mode power supply controller as a single chip. Inthe example, the single chip can comprise PFC stage 104, PWM stage 108,and FC circuit 118 as indicated by dashed lines 134. The circuitry canbe more or less than shown and the integration can vary depending on thepower supply application. As shown, FC circuit 118 can have a node 120,a node 122, a node 124, and a node 126. Node 120 corresponds to avoltage HV that can be provided by FC circuit 118. A capacitor 128 canbe coupled to node 120 to store energy. In the example, the currentprovided during the start mode from the off-mode can be provided by thesource of voltage HV, capacitor 128, or both. A feedback pin or feedbacknode of the switch mode power supply controller corresponds to node 122of FC circuit 118. A circuit 130 can be coupled to the output 102A orthe Vcc 102 of the switching power supply 100. The circuit 130 generatesa signal corresponding to the voltage Vout. The circuit 130 can furtherinclude circuitry for detecting the loading on the output 102A. Thevoltage Vout at output 102A can be a high voltage like 19 V used forAdaptors. In one embodiment, circuit 130 optically can be coupled to afeedback device 132. As shown, feedback device 132 can be a transistorthat generates a current that corresponds to the voltage Vout, loadingat output 102A, or both. The collector of the feedback device 132 can becoupled to the node 122. The FC circuit 118 also receives the voltageVcc from the output 102 of switching power supply at node 124.Additionally, FC circuit 118 can have a node 126 that can be coupled toPFC stage 104 and PWM stage 108. The FC circuit 118 generates a drivesignal that enables or disables the switch mode process thatrespectively transfers energy to the output 102A or prevents energytransfer from occurring.

It should be noted that the configuration of switching power supply 100can be used to merely illustrate the general operation of a switch modeprocess to generate a regulated voltage. Furthermore, the descriptionabove can be an example of how the off-mode influences the powerefficiency of the power supply 100. There are many types of switch modepower supplies and switch mode power supply architectures that can useoff-mode to improve long-term power efficiency. The Feedback Controlcircuitry 118 can be adapted to different types of switch mode processeswithout increasing pin count of the controller circuitry. High volumecommercial applications include low cost flyback circuits, notebookcomputer power supplies, and ATX power supplies all of which wouldbenefit from the improved efficiency. Cost and performance are a factorin the selection of the technology used. Often, the initial cost of thesupply can be chosen over the most efficient solution even thoughimproved efficiency yields a lower cost long term due to reduced energyusage. The addition of FC circuit 118 can lower cost while improvingperformance.

Thus, the FC circuit 118 can be integrated into existing switch modepower supply controllers to improve operating efficiency therebypromoting the proliferation of more efficient power supplies to reducelong-term energy consumption. Moreover, the performance and costimprovements can be achieved with no added complexity to the powersupply circuitry nor introduce changes in an assembly process. In otherwords, a performance improvement can be achieved by merely replacing theexisting switch mode power supply controller disclosed herein belowallowing rapid retrofitting for improving performance, lowering thebarrier for adoption, and lowering cost of power supply integration.

FIG. 2 is a schematic diagram of the Feedback Control circuit 118 whichcan provide off-mode without increasing pin count in accordance with anembodiment. In the example, nodes 120, 122, 124, and 128 are pins of anintegrated circuit. Nodes 120, 122, 124, and 128 respectively correspondto a voltage input, feedback, switch mode power supply Vcc supply, andcontroller drive that are either common pins or internal nodes of mostswitch mode power supply controllers thereby allowing integration of FCcircuit 118 thereto. Alternatively, nodes 120, 122, 124, and 128 can beinternal nodes of a power supply, circuit, or integrated circuit. Thesecondary side of power supply 100 comprises the secondary winding oftransformer 112A, rectifier 114A, storage capacitor 116A, error signalcircuitry, and condition or status circuitry 130 coupled thereto. Thecondition or status circuitry 130 includes the circuitry coupled tooutput 102A that can be optically coupled to transistor 132 which canprovide a signal that controls the transitions between off-mode, startmode, and regulation mode. The condition or status circuitry 130 canalso include a circuit to detect a no-load condition.

FC circuit 118 comprises a current source section 230, a startcomparator 216, and a regulation comparator 228. A voltage HV can beprovided to node 120 of the FC circuit 118. A storage capacitor 128stores charge to deliver to the current source section 230 under a startmode. The start mode discussed herein can be used to rapidly raise thevoltage at the Vcc 102 after the off-mode. The start mode can be used inother operating sequences of the switch mode power supply 100. Thevoltage HV coupled to node 120 should be greater than a regulatedvoltage at Vcc 102 of the power supply 100. The voltage HV can beregulated or unregulated. The current source section 230 comprises acurrent source 202, a current source 204, and a switch 206. In oneembodiment, the current source 202 can have a first terminal coupled tonode 120 and a second terminal coupled to the node 122. The currentsource 204 can have a first terminal coupled to the node 120 and asecond terminal. The switch 206 can have a first terminal coupled to thesecond terminal of current source 204, a control terminal, and a secondterminal coupled to the node 124. The node 124 can be coupled to the Vcc102 of the switch mode power supply 100.

The FC circuit 118 can be coupled to or include current source 204 whichcan provide current to the Vcc 102 of the power supply 100 under startmode. The start circuitry comprises zener diode or resistance 208,resistor 210, zener diode 212, and the start comparator 216. In general,the start comparator 216 includes a positive input, a negative inputcoupled to a reference voltage, and an output coupled to the controlelectrode of switch 206. In the example, a high state at the output ofstart comparator 216 closes the switch 206 thereby coupling currentsource 204 to the Vcc 102. The zener diode 208 can have a cathodecoupled to the node 122 and an anode coupled to a positive input ofstart comparator 216. Resistor 210 can have a first terminal coupled tothe positive input of start comparator 216 and a second terminal coupledto ground. The zener diode 212 can have a cathode coupled to thepositive input of the start comparator 216 and an anode coupled toground. A voltage reference 214 provides a voltage Vstart to thenegative input of the start comparator 216. The comparator 216incorporates hysteresis whereby a transition from low to high state orhigh to low state occurs at different threshold voltages.

The FC circuit 118 further includes regulation comparator 228 which canprovide a drive signal that can be coupled to the switch mode powersupply controller to enable and disable a switch mode process. Thecircuit comprises resistor 222, diode 224, and the regulation comparator228. In general, the regulation comparator 228 includes a positiveinput, a negative input coupled to a reference voltage, and an outputwhich can provide the drive signal. In the example, the power supply 100can transfer energy to the output 102 when the switch mode power supplycontroller can be enabled by the drive signal from regulation comparator228. Conversely, no energy transfer occurs at output 102 from the switchmode process when the switch mode power supply controller is disabled bythe drive signal from regulation comparator 228.

The resistor can have a first terminal coupled to receive an internalset voltage Vdd and a second terminal coupled to the positive input ofthe regulation comparator 228. The diode 224 can have an anode coupledto the positive input of the regulation comparator 228 and a cathodecoupled to node 122. A voltage reference 226 provides a voltageVregulation to the negative input of the regulation comparator 228. Theoutput of regulation comparator 228 can be coupled to node 126. Thevoltage Vdd provided to the first terminal of resistor 222 correspondsto the supplyvoltage Vcc provided to node 124 of FC circuit 118. In oneembodiment, the voltage Vdd can be translated from the voltage Vcc by acircuit. In general, the voltage Vdd can be fixed. Thus, the startcomparator 216 and the regulation comparator 228 support start,regulation, and off-mode processes via a signal applied to the feedbacknode 122.

FIG. 3 is a schematic diagram of circuitry for a start mode inaccordance with an embodiment. As mentioned previously, the start modecan occur when the power supply 100 is first turned on or from theoff-mode. In general, the voltage Vcc at the output 102 of power supply100 can be out of the predetermined voltage range maintained duringregulation. The start mode can be enabled to deliver current to theoutput 102 thereby raising the voltage thereon. A different operationalsequence can be used when initially powering up the switch mode powersupply 100. The start mode described herein can be used at least whentransitioning from the off-mode. The current from current source 204during the start mode raises the voltage Vcc at 102 to a predeterminedvoltage that starts the switch mode process.

Prior to start mode, a signal applied to node 122 sinks the current fromcurrent source 202 such that the zener diode 208 is non-conductive.Zener diode 208 is non-conductive when the voltage at node 122 isinsufficient to induce breakdown. The voltage at the positive input ofstart comparator 216 is approximately a ground potential when zenerdiode 208 is non-conductive. The reference voltage Vstart coupled to thenegative input of start comparator 216 can be greater than groundthereby generating a “0” or low state at the output of start comparator216. The low state at the output of the start comparator 216 maintainsswitch 206 in the open state such that current source 204 does notprovide current to the Vcc 102 of the power supply 100.

The voltage will rise at node 122 when the signal applied to node 122can no longer sink the current from current source 202. The voltage willrise above the breakdown voltage of zener diode 208 above apredetermined sink current applied to node 122. Zener diode 208 thenbreaks down above a predetermined voltage such that resistor 210 andzener diode 208 conduct current. The voltage at the positive input ofthe start comparator 216 will increase with increasing current conductedby resistor 210. The output of start comparator 216 switches from thelow state to a “1” or high state when the voltage at the positive inputof start comparator 216 is greater than the reference voltage 214(Vstart) coupled to the negative input of start comparator 216. The highstate at the output of start comparator 216 enables or closes the switch206 coupling the current source 204 to the node 124 and the Vcc 102 ofthe power supply 100.

As mentioned previously, the switch mode process can be off during startmode. A negative voltage differential can be generated across the +/−inputs of the regulation comparator 228 (FIG. 4) due the voltage Vddbeing less than the reference voltage 226 (Vregulation). Details will bedescribed in more detail herein below. The current from current source204 charges storage capacitor 116 thereby increasing the voltage Vcc.The magnitude of voltage HV and the charge stored on storage capacitor128 can be sufficient to rapidly raise the voltage at the output 102 toa start output voltage that initiates the switch mode process. Asdiscussed above, raising Vcc also increase Vdd. The zener diode 212clamps the voltage at the positive input of start comparator 216 fromgoing above a breakdown voltage of the zener diode 212.

FIG. 4 is a schematic diagram of circuitry for a switch mode process tomaintain the output 102A between a predetermined voltage range inaccordance with an embodiment. In the example discussed above, thecurrent from current source 204 (FIG. 3) increases the voltage Vcc atthe output 102. At a predetermined voltage at the output 102A, amagnitude can be reached where the optical diode of a condition andstatus circuitry 130 begins conducting a current. An optical signal canbe coupled to transistor 132 where it can be converted to a base currentthat corresponds to the output voltage Vout. The base current enablestransistor 132 to sink current at node 122. The base and collectorcurrent of transistor 132 increases with rising voltage Vout at output102A. The collector current of transistor 132 at the predeterminedvoltage at the output 102A can be sufficient to force the voltage atnode 122 to fall until zener diode 208 is non-conductive. Thepredetermined voltage where zener diode 208 becomes non-conductive canbe the voltage Vstart as will be discussed in more detail below. Thepositive input of start comparator 216 falls to ground via resistor 210when zener diode 208 becomes non-conductive. The reference voltage 214can be greater than the ground voltage at the positive input of startcomparator 216 producing a transition from the “1” or high state to a“0” or low state at the output of start comparator 216. The low stateopens the switch 206 decoupling current source 204 from the Vcc supply102 which prevents the voltage Vcc from increasing greater than thevoltage Vstart.

In general, the switch mode process provides power to a load and storagecapacitor 116A coupled to the output 102A. The switch mode processregulates or maintains the voltage Vout at output 102 within apredetermined voltage range. As mentioned previously, the opticalfeedback to transistor 132 corresponds to the voltage Vout at output102. The frequency or amount of energy transfer corresponds to theloading at output 102. For example, an increase in loading will producea corresponding negative rate of change at the output 102. The negativerate of change can be detected by the switch mode power supplycontroller thereby increasing the frequency or amount of energytransferred over a period of time to counter the trend and to keep thevoltage Vout above the minimum voltage of the predetermined voltagerange. In one embodiment, the increase in frequency or amount of energytransfer changes the rate of change from negative to positive therebyincreasing the voltage Vout at the output 102A. Conversely, the transferof energy can be reduced under lightly loaded conditions to stop apositive rate of change in the energy transfer that would eventuallyincrease the voltage Vout above the maximum voltage of the predeterminedvoltage range.

The regulation comparator 228 provides a drive signal to the switch modepower supply controller that enables the switch mode process to regulatethe voltage at the output 102A. In the example, this corresponds to asignal transition from no-signal at node 122 (e.g. start mode) tooptical feedback enabling transistor 132 (e.g. regulation mode) to sinkcurrent from node 122 when the voltage at supply 102 reaches the voltageVstart. In one embodiment, the output regulation comparator 228transitions from the low state to the high state after current source204 is decoupled from the Vcc 102. The positive voltage differentialfrom the positive input to the negative input of the regulationcomparator 228 can be a function of the voltage at node 122 and thevoltage Vdd at the first terminal of resistor 222. The voltage Vdd canbe the voltage Vcc or a voltage corresponding to the voltage Vcc. Forexample, the voltage Vdd can be scaled from the voltage Vcc to determinea switch point with the reference voltage 226. Vdd can also be aninternal reference voltage that is predetermined.

The voltage at node 122 during the start mode can be approximately thebreakdown voltage of zener diode 208 and the voltage across resistor210. The diode 224 becomes conductive when the voltage Vdd is greaterthan the voltage at node 122 and the forward diode voltage drop of diode224 when conducting. Prior to the transition from start mode toregulation mode, diode 224 is non-conductive. The non-conductive stateof diode 224 results in the voltage at the positive input of comparator228 being the voltage Vdd. In one embodiment, the voltage Vcc at theoutput 102 of the power supply 100 is less than a minimum regulatedvoltage prior to the start mode. The voltage Vdd corresponding to thevoltage Vcc that is less than the minimum regulated voltage can be lessthan the reference voltage 226 or Vregulation. Thus, the output ofregulation comparator 228 can be in the low state under the conditionlisted above. Note that during the start mode, the voltage Vcc at theoutput 102 of the power supply 100 can be rapidly changing due to thecurrent provided by current source 204. Thus, the low state at theoutput of comparator 228 disables the switch mode power supplycontroller from transferring energy to the Vcc supply 102 during thestart mode.

Prior to enabling the switch mode process in regulation mode, the diode224 isolates node 122 from the positive input of regulation comparator228. The diode 224 introduces an offset on the positive input ofregulation comparator 228 that does not affect performance. In oneembodiment, the transition from start mode to the regulation mode occurswhen the voltage Vcc at the output 102 reaches Vstart. The voltage Vddcan be at a voltage corresponding to Vstart. In the example, the diode224 can be conducting when the output 102 is at the voltage Vstart. Inother words, the voltage Vdd when the output 102 is at the voltageVstart is greater than the voltage at anode 122 plus a forward voltagedrop of diode 224. The voltage at the positive input of comparator 228can be approximately the voltage at node 122 plus the forward voltagedrop of diode 224. In this condition, the voltage at the positive inputof regulation comparator 228 can be greater than the regulation voltage226 or Vregulation. The output of regulation comparator 228 thentransitions from the “0” or low state to a “1” or high state. The highstate at the output of regulation comparator 228 can be coupled to theswitch mode power supply controller to enable the switch mode process.

Enabling the switch mode process allows the transfers energy to theoutput 102A of the power supply 100 and establishes regulation tomaintain the voltage Vout within the predetermined voltage range. Itshould be noted that energy transfer can be controlled by the switchmode power supply controller. The switch mode process can be enabled toallow the transfer of energy as long as the output of the regulationcomparator 228 is in the high state. The amount of feedback provided tonode 122 and the voltage Vdd operatively determines if the switch modeprocess can be enabled or disabled. In one embodiment, the output ofregulation comparator remains in the high state during the regulationmode thereby maintaining the voltage Vout at the output 102A of thepower supply 100 within a regulated voltage range.

In the case when the output 102A is lightly loaded an increase in powerefficiency can be achieved by disabling the switch mode process. Thisconfiguration can be known a skip mode or a standby mode. The switchmode process can be enabled and disabled to respectively transfer energyto the output 102A and then disable the energy transfer process. Theswitch mode power supply controller can be disabled for an extendedperiod of time depending on how light the load can be at the output102A. In the skip mode, the voltage Vout can be maintained at the lowerportion of the regulated voltage range to further minimize powerconsumption. Moreover, in at least one embodiment, while in the skipmode, the voltage Vout is not allowed to fall outside the regulatedvoltage range.

FIG. 5 is a schematic diagram of circuitry for an off-mode process inaccordance with an embodiment. In at least one embodiment, condition orstatus circuitry 130 (FIG. 2) includes an automatic no load detectioncircuit. The automatic no load detection circuit detects when there isno load coupled to the output 102A of the power supply 100. In theexample, the no load detection circuit enables the transistor 132 todrive the node 122 to approximately ground. In an alternate embodiment,the no load detection circuit can have an output coupled to node 122that drives node 122 to ground when no load is detected. In general,detecting a no-load condition at the output 102A of the power supply 100transitions the signal at node 122 to the off-mode (e.g. ground). Theswitch mode process can be disabled upon detecting the no-load conditionthereby stopping the transfer of energy to the output 102A of the powersupply 100.

The base current provided to transistor 132 when a no-load condition isdetected turns the device on such that the collector sinks currentsufficiently enough to hold node 122 at ground. Node 122 at groundrenders zener diode 208 non-conductive. The voltage at the positiveinput of start comparator 216 can be driven to ground through resistor210 when zener diode 208 is non-conductive. The voltage at the negativeinput of start comparator 216 can be greater than the voltage at thepositive input when node 122 is at ground. The output of startcomparator 216 transitions from the “1” or high state to the “0” or lowstate or remains in the low state depending on the initial condition ofstart comparator 216.

The diode 224 (FIG. 4) conducts a current when node 122 is at ground.The voltage at the positive input of the regulation comparator 228 is atapproximately the forward voltage drop of diode 224. In the example, thevoltage at the positive input of regulation comparator 228 is less thanthe reference voltage 226 coupled to the negative input. The output(e.g. drive signal) of the regulation comparator 228 can be at “0” orlow state when the reference voltage 226 is greater than the voltage atthe positive input. As mentioned previously, the drive signal in the lowstate disables or prevents the transfer of energy by a switch modeprocess to the output 102A of the power supply 100. In the off-mode,little to no energy is provided to the storage capacitor 116. Thestorage capacitor 116A will slowly discharge over time during theoff-mode due to leakage currents. Holding the node 122 at ground allowsthe voltage Vout to fall out of regulation and below the minimum voltageof the predetermined voltage range when regulated because both theoutputs of start comparator 216 and regulation comparator 228 are in thelow state. The voltage Vout continues to fall until the output 102Areaches a predetermined voltage that can be below the minimum regulatedvoltage at the output 102A in the off-mode. In one embodiment, theoutput 102A upon reaching the predetermined voltage below the minimumregulated voltage results in the condition or status circuitry 130 nolonger providing an optical signal to the transistor 132. The transistor132 is disabled or turned off when no optical signal is provided suchthat no current is conducted by the device. A transition from off-modeto start mode then occurs. The voltage at node 122 will start to risefrom current provided by current source 202. The start mode can beinitiated when zener diode 208 becomes conductive as disclosed above.The start mode can be coupled current source 204 to the Vcc supply 102stopping the discharge of storage capacitor 116 and rapidly raises thevoltage Vcc to the voltage Vstart.

FIG. 6 is a timing diagram illustrating start mode, regulation mode, andoff-mode operating cycles of the switch mode power supply controller andmore specifically the operation of FC circuit 118 in accordance with anembodiment. FIGS. 1 and 2 can be referred to when describing circuitcomponents. The status of the circuitry of FC circuit 118 will be usedto describe operational changes that result in the different modes beingimplemented through the feedback pin or feedback node of the powersupply 100. Prior to A the power supply can be off and the voltage HV isnot provided to node 120. At step A, voltage HV is provided to node 120,voltage Vcc is at ground, and the transistor 132 is off. In the example,the voltage HV can be greater than the maximum regulated voltage VccStart The outputs of both the start comparator 216 and the regulationcomparator 228 can be in a low state such that the switch mode powersupply controller is disabled from transferring energy to the output102A. No feedback signal is provided to node 122. The start mode can beinitiated by FC circuit 118 when the output of comparator 216transitions from the low state to a high state. The output of comparator228 remains in the low state preventing the transfer of energy by theswitch mode process. The start mode couples the current source 204 tothe node 102 and charges the storage capacitor until the voltage Vcc atnode 102 equals the voltage Vcc Start.

At step B, the regulation mode can be initiated by FC circuit 118. Theoutput of comparator 216 transitions from the high state to the lowstate when the supply 102 reaches the voltage Vcc Start. The transistor132 can be enabled through the optical feedback corresponding to thevoltage at the output 102A. Transistor 132 provides the feedback signalto node 122. The current source 204 can be decoupled from the node 102of the power supply 100 preventing further increase in the voltage Vcc.

The feedback signal at node 122 and an increase in the voltage Vddproduces a change in comparator 228. The output of comparator 228transitions from the low state to the high state providing a drivesignal for enabling the switch mode power supply controller to transferenergy to the output 102A as required by the switch mode process.Although the switch mode power supply controller is enabled, no transferof energy occurs in step B. The voltage Vcc falls after step B from thepeak voltage Vcc Start due to loading on the supply 102 of the powersupply 100 until the switch mode process transfers energy to maintainregulation.

From step C to step D, the power supply 100 operates in the regulationmode as a normal switching power supply. The switch mode power supplycontroller controls the frequency or amount of energy transfer tomaintain the voltage Vout at the output 102A to the requested andregulated value. The supply Vcc is kept between the voltage Vcc Startand the voltage Vcc Stop. The rate of energy transfer will vary withvariations in loading. The regulation mode maintains the voltage Vout atthe output 102 within this range when the switch mode process isenabled. Optical feedback corresponding to the voltage Vout and morespecifically to a voltage within the regulated voltage range can beprovided during regulation. The feedback signal to node 122 and thevoltage Vdd enable the switch mode process. Thus, the output ofcomparator 228 stays in the high state (e.g. drive signal) duringregulation thereby providing the drive signal to sustain the regulationmode operation of FC circuit 118. The output of the start comparator 214remains in the low state during regulation due to the voltage Vcc atsupply 102 being greater than Vcc Stop. Current source 204 can bedecoupled from the Vcc supply 102.

In step D, a lightly loaded condition occurs where keeping the switchmode process enabled would decrease the power efficiency. The lightlyloaded condition can be also called standby or skip mode. In skip mode,the voltage supply Vcc declines at a much slower pace when a normal loadis coupled to the output 102A. The output of comparator 228 transitionsfrom the high state to a low state when the skip or standby mode isinitiated in the step D. The drive signal in the low state disables theswitch mode power supply controller from transferring energy to theoutput 102A.

In step E, the power supply 100 can be in the skip or standby mode. Theoutput 102A can be lightly loaded allowing an extended period of timebefore the transfer of energy is required to maintain regulation. In theskip mode, the switch mode process can be enabled before the voltage Vccfalls to Vcc stop or below. A signal can be provided to the node 122that transitions the regulation comparator 228 from the low state to thehigh state. The drive signal in the high state enables the switch modepower supply to engage the switch mode process. The transfer of energyto the output 102A of the power supply 100 by the enabled switch modeprocess raises also the voltage Vcc as shown in step E.

In a step F, the lightly loaded condition continues to exist. Referringback to step E, energy was transferred to raise the voltage Vout. Theskip mode can be reinstated upon detecting the lightly loaded condition.The output of comparator 228 transitions from the high state to a lowstate upon initiating the skip mode similar to step D. The drive signalin the low state disables the switch mode power supply controller fromtransferring energy to the output 102A.

In a step G, the power supply 100 is in the skip or standby mode. Theoutput 102A can be lightly loaded allowing an extended period of timebefore the transfer of energy can be required to maintain regulation. Asdisclosed in step E, the switch mode process can be enabled before thevoltage Vcc falls to Vcc stop or below. A signal can be provided to thenode 122 that transitions the regulation comparator 228 from the lowstate to the high state. The drive signal in the high state enables theswitch mode power supply to engage the switch mode process. The transferof energy to the output 102A of the power supply 100 by the enabledswitch mode process raises the voltage Vout as shown in step G.

In step H, a no-load condition can be detected at the output 102A. Thedetected no-load condition initiates an off-mode by FC circuit 118. Theoff-mode transitions the node 122 to ground. The node 122 at groundholds the outputs of comparator 214 and comparator 228 in the low state.The switch mode process is disabled preventing the transfer of energy tothe output of 102A. The off-mode differs from the skip mode by allowingthe voltage Vcc at the supply 102 to fall below the voltage Vcc Stopcorresponding to the minimum voltage under regulation.

In a step I, the voltage Vcc can have fallen below the voltage Vcc Stop.A start mode can be initiated when the optical feedback collapses due tothe voltage at output 102A or when the signal enabling transistor 132 tohold node 122 ground is removed. In either case, the start mode can beinitiated because no signal is provided to node 122. The startcomparator 216 transitions from the low state to the high state whenno-signal is applied to node 122. The current source 204 is then coupledto the supply 102 thereby raising the voltage Vcc. The off modetransitions to the start mode when the current source 204 raises thevoltage at the Vcc supply to 102 Vcc Start.

The voltage Vcc Start on the supply 102 enables optical feedback to thetransistor 132. The transistor 132 reduces the voltage on node 122causing the start comparator 216 to transition from the high state tothe low state. The low state at the output of start comparator 216decouples the current source 204 from Vcc supply 102 thereby preventinga further increase in the voltage Vcc. The voltage on node 122 causesthe output of regulation comparator 228 to transition from the low stateto the high state. The drive signal in the high state enables the switchmode power supply controller to transfer energy to the output 102A ifrequired. The voltage Vcc at Vcc start allows SMPS to transfer energy tooutput 102A as requested by level of node 122. The voltage Vcc declinesover an extended period of time to the level corresponding to theregulation level (lower than Vcc start). As discussed above, the switchmode process or regulation mode can be enabled during step I and willregulate the voltage VoutNote that the initiated start mode allows thesystem to be supplied to be able to regulate the output voltage bytransferring the energy requested to keep the output voltage to therequested level.

In a step J, the power supply 100 changes from the regulation mode tothe off-mode. In one embodiment, the regulation mode transitions throughthe skip mode and then to off-mode. A lightly loaded condition can bedetected and the skip mode can be initiated. In the skip mode, thesignal at node 122 causes the output of the regulation comparator 228 totransition from the high state to the low state. In other words, thesignal at node 122 can be less than a skip level that initiates the skipor standby mode. The drive signal in the low state disables the switchmode power supply controller from transferring energy to the output102A. The voltage Vout continues to decline over an extended period oftime. A no-load condition can be detected prior to transitioning to aregulation mode during the skip mode. The detection of the no-loadcondition initiates the off-mode that transitions the node 122 toground. The voltage Vcc can be then allowed to fall below Vcc Stop asshown in step J. The current source 204 remains decoupled from supply(node 102) during the skip mode and the off-mode.

In a step K, the voltage Vcc can have fallen below the voltage Vcc Stopsimilar to step I. The start mode can be initiated because no signal canbe provided to node 122. The start comparator 216 transitions from thelow state to the high state when no-signal can be applied to node 122.The current source 204 is then coupled to the output 102 thereby raisingthe supply voltage Vcc. The start mode transitions to the regulationmode when the current source 204 raises the voltage at node 102 to VccStart.

The voltage Vcc Start on the node 102 enables optical feedback to thetransistor 132. The transistor 132 reduces the voltage on node 122causing the start comparator 216 to transition from the high state tothe low state. The low state at the output of start comparator 216 decanbe coupled the current source 204 from node 102 thereby preventing afurther increase in the voltage Vcc. The voltage on node 122 causes theoutput of regulation comparator 228 to transition from the low state tothe high state. The drive signal in the high state enables the switchmode power supply controller to transfer energy to the output 102A ifrequired. The voltage Vcc at Vcc start supply the SMPS to allow transferof energy if needed. The voltage Vout declines over an extended periodof time as no energy is transferred to the output 102A but the switchmode process remains enabled.

In a step L, the output 102 can be loaded. The signal on node 122 doesnot decline to a level where a skip mode can be initiated. The output ofthe regulation comparator remains in the high state to continue theswitch mode process. The drive signal in the high state keeps the switchmode power supply controller in the regulation mode. Energy can betransferred the switch mode process to the output 102A to maintain theoutput to the requested regulation level while the drive signal remainsin the high state.

FIG. 7 is a timing diagram illustrating the switch mode power supplycontroller in the off-mode implemented through a feedback pin orfeedback node in accordance with an embodiment. FIGS. 1 and 2 can bereferred to when describing circuit components. Prior to the step I, theFC circuit 118 can be in the off-mode. The outputs of start comparator216 and regulation comparator 228 can both be in the low state. Thevoltage Vout at the output 102A of the power supply 100 falls below theminimum regulated voltage in the off-mode. In the step I, a start modecan be initiated when the optical feedback collapses due to the voltageVout at output 102A or when the signal enabling transistor 132 to holdnode 122 ground is removed. In either case, the start mode is initiatedbecause no signal can be provided to node 122. The voltage on node 122(e.g. feedback pin or feedback node) begins to rise by the currentprovided by current source 202 driving the high impedance of node 122.

In a step I1, the voltage at node 122 rises to a voltage that breaksdown zener diode 208 thereby making it conductive. The output of startcomparator 216 transitions from the low state to a high state when zenerdiode 208 is conductive. The voltage at node 122 when zener diode 208becomes conductive is shown as the voltage HV control. The output ofstart comparator 216 in the high state can be coupled the current source204 to the Vcc supply (e.g, node 102) of power supply 100. The currentfrom current source 204 rapidly increases the voltage Vcc at node 102.Optical feedback corresponding to the voltage Vcc enables the transistor132 for conducting a current. The enabled transistor 132 sinks currentfrom current source 202 and reduces the voltage at node 122. The voltageat node 122 can be reduced by the optical feedback to make zener diode208 non-conductive. The output of the start comparator 216 transitionsfrom the high state to the low state when zener diode 208 can benon-conductive. The low state at the output of the start comparator 216decan be coupled the current source 204 from the supply 102 when theoutput 102 can be at the voltage Vcc Start.

In a step I2, the voltage at node 122 in combination with the supply 102at Vcc Start produces a transition from the low state to a high state atthe output of regulation comparator 228. The drive signal in high stateenables the switch mode power supply controller to transfer energy viathe transformer 112. Thus, the power supply 100 changes from the startmode to the regulation mode. In one embodiment, the optical feedback canbe clamped high until the regulation starts to be activated on thesecondary side of the power supply 100. In general, increasing opticalfeedback reduces the rate of energy transfer over a period of time. Thevoltage Vcc decreases at output 102 as little or no energy transferoccurs to output 102A during the step I2.

In step I3, the voltage Vcc decreases from Vcc start to regulated levelcorresponding to level of output voltage on 102A Lowering the opticalfeedback increases the rate of energy transfer over a period of time.Energy can be transferred by the switch mode process to the output 102Aat a rate that increases or prevents both Vout and the voltage Vcc fromdecreasing further. The energy transfer can be provided from thesecondary side of transformer 112.

In the step J, the optical feedback continues to go down. In theexample, the feedback level goes less than a skip level. The secondaryno-load detection circuit in condition and status circuit 130 (FIG. 2)detects a no-load condition during step J. The condition and statuscircuit 130 in the off-mode enables transistor 132 to drive the node 122at ground. The power supply 100 changes from the regulation mode to theoff-mode. The low feedback level causes the output of the regulationcomparator to transition from the high state to the low state. The drivesignal in the low state disables the switch mode power supply controllerfrom transferring energy to the output 102A of power supply 100. Thevoltage Vcc will continue to fall as no energy can be transferred tomitigate charge loss. As shown, the voltage Vcc decreases to the voltageVcc Stop from step J to step J1.

In step J1, the condition and status circuit 130 maintains the node 122in the off-mode such that the voltage Vcc at the supply 102 continues tofall below the voltage Vcc Stop. The voltage Vcc continues to fall untilthe optical feedback collapses due to the voltage Vout at output 102A orwhen the signal enabling transistor 132 to hold node 122 ground isremoved. In the example, the transistor 132 can be turned off when theoptical feedback collapses. The voltage at node 122 rises to change thepower supply 100 from the off-mode to the start mode indicated again bythe step I. The process continues again as discussed above.

FIG. 8 is a schematic diagram of the FC circuit 118 including anexternal pull-up in accordance with an embodiment. A diode 814 can havean anode coupled to the secondary transformer winding and a cathode to astorage capacitor 824 can have a first terminal coupled to the cathodeof diode 814 and a second terminal coupled to ground. A voltage Vcc1corresponds to the voltage on the cathode of diode 814. In oneembodiment, the storage capacitor 824 can have a capacitance less thanthe storage capacitor 116. The voltage Vcc1 corresponds to the voltageVcc as both are generated by the auxiliary winding of the switch modepower supply.

The external pull-up comprises a diode 830 and resistor 840. The diode830 can have an anode coupled to the cathode of the diode 814 and acathode to the resistance R840. The resistor 840 includes a firstterminal coupled to the cathode of diode 830 and a second terminalcoupled to the node 122. A current is conducted by the diode 830 whenthe voltage Vcc1 is more than a forward diode voltage drop above thevoltage at node 122. Thus, current to raise the voltage at node 122comprises the current from current source 202 and the current providedthrough the external pull-up. The external pull-up coupled to thefeedback pin or feedback node (e.g. node 122) provides several benefits.First, there is reduced pull-up when the power supply 100 is inoff-mode. Second, the resistor 840 increases the pull-up in the ON modebut the amount of charge is limited during starting phase while the capis discharged. Third, storage capacitor 824 including a low capacitancevalue provides reduced pull-up in the low frequency skip mode as cap isdischarged in between 2 cycles. Finally, requirements for the opticallygenerated current by transistor 132 and secondary drive current can bereduced. These benefits result in improved skip or standby mode. Powerconsumption can be reduced in both the standby mode and the off-modethereby improving the long-term efficiency of the power supply 100. Afurther improvement can be incorporated by adding an internal pull-upswitch controlled by the skip mode control.

FIG. 9 schematically illustrates an embodiment of a portion of anintegrated circuit including an off-mode detection circuit 910. Theoff-mode detection circuit 910 includes at least two comparators 940 and942, several resistors 930, 932, diode 962, current source 914, AND gate980, inverter 960, and reference voltage 950. The feedback signal entersthrough pin 920 and if the feedback signal is high then HV source viapin 922 supplies through current source 912 the Vcc when collapsing froma transformer. In the IC illustrated, Vcc is provided through pin 924,the driver signal through pin 926, and the IC is grounded via pin 928. Afurther current source 912 is connected to a regulation module 970 whichis operatively connected to a reference Vdd, another current source 916and diode 964. Diode 964 is operatively connected to a resistor 934which is connected to node (pin) 920 and to the positive terminal ofcomparator 944. The opposite terminal of current source 916 is connectedto the negative terminal of comparator 944 and voltage reference 952.The comparator 944 result is connected operatively to the SMPS controlpart to drive the Power Switch through pin 926.

FIG. 10 is a schematic diagram of the FC circuit 118 which can providepower factor correction feedback in accordance with an embodiment. Forbrevity, only the added circuitry to FC circuit 118 will be discussed. Apath for coupling current source 204 between the node 120 and node 124can be controlled by two switches. The added switch allows the HVvoltage to be used as power factor correction feedback. The two switchesalso provide low OFF mode consumption by disconnection of current source204 in standby mode or off mode. Switch 206A can have the first terminalcoupled to the node 120 and the control terminal coupled to the outputof the start comparator 216. The current source 204 can have the firstterminal coupled to the second terminal of the switch 206A. Operation ofthe switch 206B operates similarly to that described hereinabove by thestart comparator 216 with regards to switch 206B. A switch 206A can beadded to the FC circuit 118. The switch 206B can have a first terminalcoupled to the second terminal of the current source 204, a controlterminal coupled to a first terminal of Vcc control circuit 904 and asecond terminal coupled to the node 124. The Vcc control circuit 904 canhave a second terminal coupled to the node 124.

The switch 206B can be closed in start mode when little or no signal isprovided to node 122 thereby allowing the voltage on node 122 to rise toa level that transitions the output of start comparator 216 from the lowstate to the high state. Closing switch 206B couples the current source204 for receiving the voltage HV at node 120. Furthermore, the voltageHV at node 120 can be provided as power factor correction feedback tothe switch mode power supply controller when the switch 206A is closed.Conversely, the switch 206B can be open in the skip mode and the offmode when the voltage on node 122 falls below the reference voltage 214.Including switch 206B which decouples the current source 204 from thenode 124. In one embodiment, the reference voltage 214 can be reduced toa lower level than the application described hereinabove. Reducing thereference voltage 214 keeps the switch 206B closed during the startmode.

The Vcc control circuit 904 controls the operation of switch 206B. TheVcc control circuit 904 detects or senses the voltage Vcc at node 124.The detection circuitry in Vcc control circuit 904 provides a controlsignal to supply 102 that corresponds to the voltage Vcc. The Vcccontrol circuit 904 provides a control signal that opens switch 206Bwhen the voltage Vcc at node 124 can be greater than a predeterminedvalue thereby decoupling current source 204 from node 124. The Vcccontrol circuit 904 provides a control signal that closes switch 206Bwhen energy can be requested. For example, energy can be requested whenthe power supply 100 can be first turned on or a transition fromoff-mode to the start mode.

FIG. 12 is a schematic diagram of the FC circuit 118 with an externalvoltage supply in accordance with an embodiment. An external voltagesupply can be coupled to node 120. In one embodiment, the externalvoltage supply can be a lower voltage than that generated by the switchmode power supply 100 in previous solutions explained. In the example,including the external voltage supply allows an embedded off mode to beimplemented. A start control can also be combined with feedback. Thelower voltage of external voltage supply at node 120 allows asimplification of circuitry and a lower component count of the FCcircuit 118. In particular, a resistor 1244 replaces current source 202.The resistor 1242 also eliminates the need for resistor 210 and zenerdiode 208 that support high voltage operation. The resistor 1242 canhave a first terminal coupled to the node 120 and a second terminalcoupled to the node 122. The FC circuit 118 operates similarly in startmode. No signal can be coupled to node 122 from transistor 132 allowingthe resistor 1242 to raise the voltage on node 122.

The external discrete off mode circuit 1200 can have a first terminalcoupled to the collector of transistor 132 and a second terminal coupledto node 124. The discrete off mode circuit 1200 comprises resistors1240, 1242, 1244, 1246, and 1248, pnp transistor 1220, npn transistor1222, diode 1250, and diode 1252. The resistors 1240 and 1106 form aresistor divider for setting a voltage at the emitter of npn transistor1222. The resistor 1242 can have a first terminal coupled to the node120 and a second terminal. The resistor 1240 can have a first terminalcoupled to the second terminal of resistor 1242 and a second terminalcoupled to ground. Base current to npn transistor 1222 can be providedthrough resistor 1246. The resistor 1246 can have a first terminalcoupled to the node 120 and a second terminal coupled to the base of pnptransistor 1222. The resistor 1244 can be an emitter degenerationresistor for pnp transistor 1220. The resistor 1244 can have a firstterminal coupled to node 120 and a second terminal. The pnp transistor1220 provides current to charge the storage capacitor 116 and raise thevoltage Vcc on node 102 when a start mode can be initiated. The currentoutput by the pnp transistor 1220 corresponds to the voltage acrossresistor 1244. The voltage across resistor 1244 and the base-emitterjunction of pnp transistor 1220 can be equal to the forward voltage dropof diodes 1250 and 1252. The diodes 1250 and 1252 are in series. The pnptransistor 1220 can have an emitter coupled to the second terminal ofresistor 1244, a base, and a collector coupled to the second terminal ofcircuit 1200. The diode 1250 can have an anode coupled to the node 120and cathode. The diode 1252 can have an anode coupled to the cathode ofdiode 1250 and a cathode coupled to the base of pnp transistor 1220. Thenpn transistor 1222 sinks the base current of pnp transistor 1220 whenenabled in the start mode. The resistor 1112 can have a first terminalcoupled to the base of pnp transistor 1220 and a second terminal. Thenpn transistor 1222 can have a collector coupled to the second terminalof resistor 1112, the base coupled to the first terminal of circuit1200, and the emitter coupled to the second terminal of resistor 1240.An external diode 1100 replaces diode 224 coupled to regulationcomparator 228. The external diode 1100 isolates the circuit 1200 fromthe node 122 of FC circuit 118. The external diode 1100 can have ananode coupled to node 122 and a cathode coupled to the first terminal ofcircuit 1200. In the start mode, the output of the regulation comparator228 is in the low state and the transistor 132 can be off. The voltageon the base of npn transistor 1222 rises by current provide throughresistor 1246. The npn transistor 1222 enabled provides base current tothe pnp transistor 1220 thereby enabling the device. The circuit 1200provides a current from the second terminal to the Vcc supply 102 of thepower supply 100. Conversely, transistor 132 when enabled such as inoff-mode, skip mode, or regulation mode sinks a current that pulls thevoltage at the base of npn transistor 1222 to a voltage that turns thedevice off. No base current can be provided to the pnp transistor 1220when the npn transistor 1222 is off such that no current can be providedto output 102 by the circuit 1200. The regulation comparator 228 is in alow state or high state depending on the mode of operation as disclosedabove. The external discrete off mode circuit 1200 keeps Vcc used for anX2 capacitors discharge function even in off mode. The internal voltageVdd can be switched off during the off mode to reduce power consumption.The off mode can be implemented when the feedback corresponding totransistor 132 is at a low level thereby improving long term powerefficiency of the power supply by allowing the voltage Vcc to fall belowVcc Stop.

FIG. 13 schematically illustrates an embodiment of a portion of a systemin accordance with an embodiment of the present invention. Illustratedis a schematic diagram of an OFF control circuit which is configured toswitch OFF a PFC IC through. FIG. 14 schematically illustrates anembodiment of a portion of a system in accordance with an embodiment ofthe present invention;

FIG. 15 schematically illustrates an embodiment of a portion of anintegrated circuit that can be a portion of a system in accordance withan embodiment of the present invention;

FIG. 16 schematically illustrates an embodiment of a portion of anintegrated circuit that can be a portion of a system in accordance withan embodiment of the present invention; and

FIG. 17 illustrates a portion of the operation of a portion of a systemof an embodiment. Various operations at specifics steps will bediscussed. At step AA the HV power supply is triggered by the feedbacksignal of positive slope in time passing a value equal to about HVControl. The HV Supply is ON until Vcc=Vcc start at which time a drivesignal is started at step BB and the system enters start-mode. At stepBB Vcc=Vcc start, and the HV Supply is switch OFF and IC started withthe initiation of a drive signal, while Vcc drops below Vcc Start. Bystep CC, ON mode is initiated by a constant feedback signal (FB). Atstep CC the system is in ON mode, FB>skip level, Vcc is regulated fromthe transformer, and the HV power supply is OFF while Vcc>Vcc stop. Inthe light load skip mode initiation at step DD there exists a lightload, FB<skip level, and Vcc is dropping but staying above Vcc stop.When the feedback signal exceeds the skip level a drive signal isinitiated that increases Vcc with energy from a transformer, this isillustrated in step EE. When the feedback signal drops below the skipvalue then the drive signal is stopped, and Vcc starts to drop again, asillustrated in step FF. As long as a light load is indicated Vcccontinues to drop. If no load is detected, such as when the feedbacksignal is below a lower threshold 1700 (e.g., skip level), then Vcccontinues to drop without any attempt to regulate. When Vcc drops below1710 a lower threshold level such as Vcc Stop then at least oneembodiment initiates an off control signal 1720 that provides power fromthe HV Supply that increases 1710 Vcc above Vcc Stop so that Vcc doesnot collapse. At step HH, when Vcc is equal to or exceeds Vcc Start theHV Supply is stopped, allowing Vcc to drop. If the feedback signal isstill less than a skip value the system remains in the off mode and Vccgradually decreases. If the secondary voltage is too low the Optocollapse or OFF signal disappears (1740), asking for restart and endingthe OFF mode. In this case the FB signal is going up again thanks to Vccpull-up. When FB>HV Control (1730), OFF control is going down and VddSupply is switched ON again. FB is going up to clamp until the start ofa regulation-mode activated from secondary side. As illustrated at stepJJ driven by the secondary regulation, FB is going down <skip level, Vccis going down as Drive is OFF. After a time, Secondary No load detectionprovides an OFF signal which keeps the FB<skip level. HV Supply will bestarted when necessary to keep Vcc above Vcc Stop. When the slope of thefeedback signal is positive in time and the feedback signal exceeds HVControl the OFF signal is stopped, the Vdd signal is started and is thedrive signal, indicating the onset of the ON mode, as illustrated instep KK. If the feedback signal has dropped then remains stable above HVControl then the feedback signal is greater than the skip value and Vccis directly supplied from transformer, as illustrated in step LL

A method of implementing an off mode, regulation mode, and start mode ina switch mode power supply through a feedback pin or feedback node of aswitch mode power supply controller is disclosed herein in one or moreembodiments. The steps disclosed can be performed in any order orcombination. In a first step, a no-load condition can be detected. Inone embodiment, a no-load condition is where an output of the powersupply is not loaded by a device requiring power. Examples of a no-loadcondition are a device coupled to the output that is turned off, thedevice in sleep-mode, the device in energy saving mode, or no devicecoupled to the output. In one embodiment, a circuit coupled to theoutput of the power supply detects the no-load condition. In a secondstep, an off mode signal is provided to the feedback pin or the feedbacknode. In the embodiment, disclosed hereinabove, the off mode signal canbe coupled to base of a transistor that pulls the feedback pin or thefeedback node to a low state or ground.

The low state at the feedback pin or feedback node can be coupled topositive input a start comparator. In a third step, a low state can begenerated at an output of the start comparator when the off mode signalcan be provided. A negative voltage differential can be created frompositive to negative input of the start comparator resulting in the lowstate at the output of the start comparator. The low state at the outputof the start comparator decoupled a current source from the output ofthe power supply. Thus, no start current is provided to the output ofthe power supply to raise the voltage thereon.

The low state of the feedback pin or feedback node also can be coupledto a positive input of a regulation comparator. In a fourth step, a lowstate can be generated at an output of the regulation comparator whenthe off mode signal is provided. A negative voltage differential can becreated from the positive to negative input of the regulation comparatorresulting in the low state at the output of the regulation comparator.The low state at the output of the regulation comparator disables theswitch mode power supply controller. In other words, the low state atthe output of the regulation comparator disables the switch mode processfrom transferring energy to the output of the switch mode power supply.Thus, no energy transfer occurs due to the switch mode process of theswitch mode power supply. Providing no charge to the output of the powersupply will result in the voltage falling below the minimum regulatedvoltage.

In a fifth step, the off mode signal is removed from the feedback pin orthe feedback node when the voltage at the output of the power supplyfalls below an off mode output voltage. In general, the voltage at theoutput is prevented from falling below the off mode output voltage. Theoff mode output voltage can be below the minimum voltage when the switchmode power supply is in regulation mode. The off mode increases thepower efficiency by extending the time between energy transfers whenpower or regulated voltage is not needed.

In a sixth step, a high state can be generated at the output of thestart comparator. In one embodiment, removing the off mode signalresults in no signal being provided to the feedback pin or feedbacknode. The no-signal at the feedback pin or feedback node results in ahigh state being generated at the feedback pin or feedback node. In theembodiment, the transistor that can be coupled to the feedback pin orthe feedback node can be turned off thereby generating no-signal. Acurrent source coupled to the feedback pin or feedback node generates ahigh state thereon. A positive voltage differential is created from thepositive to negative input of the start comparator resulting in the highstate at the output of the start comparator.

In a seventh step, the high state at the output of the start comparatorenables a current source to be coupled to the output of the switch modepower supply. The voltage at the output of the switch mode power supplywill rise due to the current supplied by the current source. In theexample, the regulation comparator does not change state from the lowstate. The high voltage at the feedback pin or feedback node and theoutput voltage of the switch mode power supply below the minimumregulated voltage maintains a negative voltage differential from thepositive to negative input of the regulation comparator.

In an eighth step, a regulation mode signal is provided to the feedbackpin or the feedback node as the voltage rises at the output of the powersupply due to the current provided by the current source in the startmode. In one embodiment, the voltage at the output of the power supplycan be rapidly charged by the current source. The regulation mode signalcan be a feedback signal that corresponds to the voltage at the outputof the power supply. More specifically, a signal corresponding to thevoltage at the output of the power supply can be optically generated andcoupled to the base of the transistor including the collector coupled tothe feedback pin or the feedback node. The signal provided to the baseof the transistor generates a collector current that can be theregulation mode signal. As mentioned previously, the regulation modesignal will vary as the voltage at the output of the power supplyvaries.

In a ninth step, a low state at the output of the start comparator canbe generated when the regulation mode signal can be provided to thefeedback pin or feedback node. The regulation mode signal reduces thevoltage at the feedback pin or feedback node such that a negativevoltage differential can be created from the positive to negative inputof the start comparator. The low state at the output of the startcomparator can decouple the current source from the output of the powersupply thereby preventing a further increase in voltage. The currentsource can be stopped or prevented from providing current to the outputof the power supply. In one embodiment, the current source can bedecoupled from the output of the power supply at approximately or beforethe voltage reaches the maximum regulated voltage.

In a tenth step, a high state at the output of the regulation comparatorcan be generated. In the example, two conditions exist in the regulationmode. First, the voltage at the output of the power supply can begreater than the minimum regulated voltage. Second, the voltage at thefeedback pin or feedback node can have transitioned from the high statein start mode to a lower state due to the regulation mode signal. Thetwo conditions combine to generate a positive voltage differential fromthe positive to negative input of the regulation comparator. Thepositive voltage differential causes the output to transition from thelow state to a high state. The high state at the output of theregulation comparator enables the switch mode power supply controller.

In an eleventh step, energy can be transferred via the switch modeprocess to maintain the voltage at the output of the power supplybetween the minimum and maximum regulated voltage. The switch modeprocess monitors the voltage at the output of the power supply andmaintains the voltage between the minimum and maximum regulatedvoltages. The frequency and amount of energy transfer can vary as afunction of loading on the output of the power supply. As disclosedherein, the transition between different operating modes can beaccomplished without adding pins to a switch mode power supplycontroller. The off-mode can then be implemented into existing designswithout printed circuit board redesigns or major part changes therebyallowing rapid adoption of more power efficient power supplies.

In at least one embodiment despite that V_(cc) is lower than requestedlevel in OFF mode no energy is transferred by the transformer to supplythe IC, where the HV Source generator will not be activated whenFeedback/ON/OFF control is below HV Control level which is above theFeedback skip level.

While embodiments have been described with reference to particularembodiments, those skilled in the art will recognize that many changesmay be made thereto without departing from the spirit and scope ofembodiments. Each of these embodiments and obvious variations thereofcan be contemplated as falling within the spirit and scope of theinvention.

What can be claimed is:
 1. A semiconductor voltage controllercomprising: a start-mode circuit associated with a start-mode; and anoff-mode circuit associated with an off-mode, where the voltagecontroller can be configured to receive a feedback signal and anoff-mode signal from a single input and provide an output voltage, wherethe voltage controller can be configured to be in the off-mode when thefeedback signal is less than a skip level and the feedback signal isless than a HV control level, and where the voltage controller can beconfigured to be in start mode when the feedback signal is greater thanHV control level and Vcc is below a Vcc-start.
 2. The voltage controlleraccording to claim 1, where the voltage controller can be configuredwhen in the off mode to start generating a drive signal and a voltagesupply signal if the feedback signal is greater than HV-control level,where the voltage controller can be configured to stop the voltagesupply signal when Vcc is about equal to Vcc-start, and where thevoltage controller can be configured to stop the drive signal when thefeedback signal is less than about a reg-low value corresponding to skiplevel.
 3. The voltage controller according to claim 1, where the voltagecontroller can be configured when in the off mode to start generating avoltage supply signal and a drive signal if the slope of the feedbacksignal in time is positive and if the feedback signal is equal to aboutHV-control level, where the voltage controller can be configured to stopthe voltage supply signal when Vcc is about equal to Vcc-start, andwhere the voltage controller can be configured to stop the drive signalwhen the slope of the feedback signal is negative and the feedbacksignal is about equal to a reg-low value corresponding to skip level. 4.The voltage controller according to claim 1, where the voltagecontroller can be configured when in the off mode to start generating avoltage supply signal if the slope of the feedback signal in time ispositive and if the feedback signal is equal to about HV-control level,where the voltage controller can be configured to stop the voltagesupply signal when Vcc is about equal to Vcc-start, and where thevoltage controller can be configured to start a drive signal when Vcc isabout equal to Vcc-start and stop the drive signal when the slope of thefeedback signal is negative and the feedback signal is about equal to areg-low value corresponding to skip level.
 5. The voltage controlleraccording to claim 1, where the voltage controller can be configuredwhen in the off mode to start generating a voltage supply signal if Vccis equal to about Vcc-stop, where the voltage controller can beconfigured to stop the voltage supply signal when Vcc is about equal toVcc-start, and where the voltage controller can be configured to start adrive signal when the slope of the feedback signal in time is positiveand the feedback signal is about equal to a the HV-control level, wherethe voltage controller can be configured to stop the drive signal whenthe slope of the feedback signal is negative and the feedback signal isabout equal to a reg-low value corresponding to skip level.
 6. Thevoltage controller according to claim 1, where the voltage controllercan be configured to start generating a supply voltage signal when aslope of the feedback signal in time is positive and the feedback signalis equal to about the HV-control level and to stop generating the supplysignal when Vcc is about equal to Vcc-start.
 7. The voltage controlleraccording to claim 1, where Vcc is lower than a requested level in OFFmode, where no energy is transferred by the transformer to supply theIC, and where the HV source generator is not activated whenFeedback/ON/OFF control is below HV Start level which is above the skiplevel.
 8. The voltage controller according to claim 6, where the voltagecontroller can be configured to generate a drive signal during the startmode when Vcc is equal to Vcc-start.
 9. The voltage controller accordingto claim 8, further comprising: a standby circuit associated with astandby mode, where the voltage controller can be configured to switchto the standby mode when the feedback signal is less than HV controllevel and Vcc is greater than Vcc-stop.
 10. A method of controlling aswitch mode power supply comprising: inputting a feedback signal and anoff-mode signal from a single input, where the feedback signal and theoff-mode signal determine whether the switch mode power supply operatesin an off-mode; and inhibiting a start-mode when the feedback signal isless than a skip level.
 11. The method according to claim 10, furthercomprising: generating a drive signal and a voltage supply signal if thefeedback signal is greater than a HV-control level; stopping the voltagesupply signal when Vcc is about equal to Vcc-start; and stopping thedrive signal when the feedback signal is less than about a reg-low valuecorresponding to skip level.
 12. The method according to claim 10,further comprising: start generating a voltage supply signal and a drivesignal if the slope of the feedback signal in time is positive and ifthe feedback signal is equal to about HV-control; stop generating thevoltage supply signal when Vcc is about equal to Vcc-start; and stopgenerating a drive signal when the slope of the feedback signal isnegative and the feedback signal is about equal to a reg-low valuecorresponding to skip level.
 13. The method according to claim 10,further comprising: start generating a voltage supply signal if theslope of the feedback signal in time is positive and if the feedbacksignal is equal to about HV-control; stop generating the voltage supplysignal when Vcc is about equal to Vcc-start; start generating a drivesignal when Vcc is about equal to Vcc-start; and stop generating thedrive signal when the slope of the feedback signal is negative and thefeedback signal is about equal to a reg-low value corresponding to skiplevel.
 14. The method according to claim 10, further comprising: startgenerating a voltage supply signal if Vcc is equal to about Vcc-stop;stop generating the voltage supply signal when Vcc is about equal toVcc-start, start generating a drive signal when the slope of thefeedback signal in time is positive and the feedback signal is aboutequal to a the HV-control level; and stop generating the drive signalwhen the slope of the feedback signal is negative and the feedbacksignal is about equal to a reg-low value corresponding to skip level.15. A switch mode power supply controller including a feedback node forreceiving a feedback signal corresponding to an output voltage of thepower supply, the controller comprising: a first comparator including afirst input coupled to the feedback node, a second input coupled to afirst reference voltage, and an output where the first comparator isconfigured to initiate a start by coupling a current to an output of thepower supply; and a second comparator including a third input coupled tothe feedback node, a fourth input coupled to a second reference voltage,and a second output for enabling energy transfer to the output of thepower supply where the first and second comparators are configured tosupport start, regulation, and off-mode processes via the feedbacksignal.
 16. The switch mode power supply controller of claim 15 furtherincluding: a first current source including a first electrode configuredto receive a first supply voltage and a second electrode coupled to thefeedback node configured to deliver a current thereto; a first switchincluding a third electrode configured to receive a first voltage, acontrol electrode coupled to the output of the first comparator, and asecond terminal; and a second current source including a fourthelectrode coupled to the second terminal of the first switch and a fifthelectrode coupled to the output of the power supply.
 17. The switch modepower supply controller of claim 16 further including: a first zenerdiode including a cathode coupled to the feedback node and an anodecoupled to the first input of the first comparator; a first resistorincluding a sixth electrode coupled to the first input of the firstcomparator and a seventh electrode configured to receive a secondvoltage; and a second zener diode including a second cathode coupled tothe first input of the first comparator and a second anode configured toreceive the second voltage.
 18. The switch mode power supply controllerof claim 17 further including: a first diode including a third cathodecoupled to the feedback node and a third anode coupled to the thirdinput of the second comparator; and a second resistor including a eighthelectrode coupled to the third input of the second comparator and aninth electrode coupled to the output of the power supply.
 19. Theswitch mode power supply controller of claim 18 further including anexternal pull up on the feedback node.
 20. The switch mode power supplycontroller of claim 19 further including power factor correctionfeedback.